feat(headlines-search): add default sorting by name in search results

- Add ascending sort by 'name' for topics and sources in headlines search
- Implement consistent sorting across paginated search results

Author: fulleni

lib/headlines-search/bloc/headlines_search_bloc.dart

@@ -141,6 +141,7 @@ class HeadlinesSearchBloc
                   limit: _limit,
                   cursor: successState.cursor,
                 ),
+                sort: [const SortOption('name', SortOrder.asc)],
               );
               emit(
                 successState.copyWith(
@@ -158,6 +159,7 @@ class HeadlinesSearchBloc
                   limit: _limit,
                   cursor: successState.cursor,
                 ),
+                sort: [const SortOption('name', SortOrder.asc)],
               );
               emit(
                 successState.copyWith(
@@ -228,12 +230,14 @@ class HeadlinesSearchBloc
           rawResponse = await _topicRepository.readAll(
             filter: {'q': searchTerm},
             pagination: const PaginationOptions(limit: _limit),
+            sort: [const SortOption('name', SortOrder.asc)],
           );
           processedItems = rawResponse.items.cast<FeedItem>();
         case ContentType.source:
           rawResponse = await _sourceRepository.readAll(
             filter: {'q': searchTerm},
             pagination: const PaginationOptions(limit: _limit),
+            sort: [const SortOption('name', SortOrder.asc)],
           );
           processedItems = rawResponse.items.cast<FeedItem>();
         default: